JPH0930803A - Production of highly pure sulfuric acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing highly pure sulfuric acid highly being removed metals and sulfur dioxide as impurities therefrom. SOLUTION: This method for producing highly pure sulfuric acid contains the following processes. An absorption process: water 2 and sulfur trioxide gas 1 are brought into contact with each other in an absorption tower 6 to allow the water to absorb the sulfur trioxide gas, thus producing the sulfuric acid 7 containing the sulfur dioxide as an impurity. A transportation process: the sulfuric acid is transported with a liquid press-transporting system containing a storage tank 17, pipe 11 for supplying sulfuric acid into the storage tank 17, a pipe 19 for discharging the sulfuric acid from the storage tank 17, a pipe 13 for supplying a gas into the storage tank 17, a pipe 15 for discharging the gas from the storage tank 17, wherein the liquid-contacting parts are manufactured with non-metallic materials. And a stripping process: the sulfuric acid supplied in the transportation process is stripped with air 4 in a stripping tower 10 to separate off the sulfur dioxide contained in the sulfuric acid from the sulfuric acid, thus producing the highly pure sulfuric acid 3.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-purity sulfuric acid. More specifically, the present invention relates to impurities such as metal components and sulfurous acid gas (sulfur dioxide SO 2
₂ ) relates to a method for producing highly purified sulfuric acid that has been highly removed.

[0002]

Sulfuric acid is used as a cleaning liquid for silicon wafers used in semiconductor factories. The presence of a metal component as an impurity in the sulfuric acid used for this purpose causes a disadvantage of deteriorating the electrical characteristics of the silicon wafer. Further, if sulfurous acid gas as an impurity is present in sulfuric acid, the same inconvenience as described above occurs. Therefore, the sulfuric acid used for such an application is required to have a low metal concentration and a low sulfur dioxide concentration. However, a method for producing high-purity sulfuric acid that satisfies such requirements and can be efficiently carried out from an industrial viewpoint has not been found.

[0003]

In view of the present situation, an object of the present invention is to provide a method for producing high-purity sulfuric acid from which metal impurities and sulfurous acid gas, which are impurities, are highly removed. Exist.

[0004]

That is, the present invention provides a method for producing high-purity sulfuric acid (3) from gaseous anhydrous sulfuric acid (1) containing sulfurous acid gas as an impurity and water (2). The present invention relates to a method for producing high-purity sulfuric acid including the following steps. Absorption step: In the absorption tower (6), water (2) and gaseous sulfuric acid anhydrous (1) are brought into contact with each other to absorb the gaseous anhydrous sulfuric acid into the water so that sulfuric acid containing sulfurous acid gas as an impurity ( 7) Step of obtaining: Transporting step: a step of transporting and supplying at least a part of sulfuric acid to the following stripping step, wherein the sulfuric acid supplied from the absorption tower is cooled by a cooler (8) and then transferred to an intermediate tank (9). The sulfuric acid stored in the intermediate tank is further stored in a storage tank (17) whose liquid contact portion is made of a non-metallic material, a sulfuric acid supply pipe (11) to the storage tank, a sulfuric acid discharge pipe (19) from the storage tank, and a storage tank. For transporting sulfuric acid by a liquid pressure-feeding system including a gas supply pipe (13) to the tank and a gas discharge pipe (15) from the storage tank Stripping process: Sulfur supplied from the transportation process in the stripping tower (10). Step of obtaining the air (4) in the scan trippin ring to high purity sulfuric acid than Nisato to separate and remove sulfur dioxide in sulfuric acid from the sulfuric acid (3)

The details will be described below (see FIG. 1).

Gaseous anhydrous sulfuric acid (SO ₃ ) used as a raw material is usually commercially available and usually contains about 10 to 100 ppm by weight of sulfurous acid gas. Further, as water used as a raw material, so-called ultrapure water is preferable.

In the absorption step of the present invention, water (2) and gaseous anhydrous sulfuric acid (1) are brought into contact with each other in the absorption tower (6) so that the anhydrous gaseous sulfuric acid is absorbed in the water to act as impurities. In this step, sulfuric acid (7) containing sulfurous acid gas is obtained. As the absorption tower, a normal one such as a packed tower can be used, and the absorption tower is generally filled with a packing such as Raschig ring. In this step, for example, a method in which gaseous anhydrous sulfuric acid is supplied from the lower part of the absorption tower and ultrapure water is supplied from the upper part of the packed tower to bring them into contact with each other in the absorption tower. Here, air may be supplied from the lower part of the absorption tower for the purpose of removing the sulfurous acid gas. It should be noted that the absorption tower in this step may also be supplied with sulfuric acid recycled from the transportation step described below, and may be brought into contact with gaseous anhydrous sulfuric acid in combination with the ultrapure water.

The transporting step of the present invention is a step of transporting and supplying at least a part of sulfuric acid to the following stripping step, wherein the sulfuric acid supplied from the absorption tower is cooled by the cooler (8), and then the intermediate tank (9 ), And the sulfuric acid in the intermediate tank is further stored in the storage tank (1
7), sulfuric acid supply pipe (11) to the storage tank, sulfuric acid discharge pipe (19) from the storage tank, gas supply pipe (1) to the storage tank
3) and a step of transporting sulfuric acid by a liquid pressure feeding system including a gas discharge pipe (15) from the storage tank.

The greatest feature of the present invention resides in that sulfuric acid is transported by the liquid pressure feeding system. That is, according to the conventional method, circulation is usually performed by a centrifugal pump or the like, but according to this method, it was difficult to control the metal concentration in sulfuric acid to a sufficiently low level. As a result of studying the cause, the present inventors have found that a metal component is eluted into sulfuric acid from a liquid contact rotating part such as a bearing of a pump, thereby causing a problem of increasing the metal concentration in sulfuric acid. Furthermore, the present inventors have studied a method for solving the problem and found that the problem can be solved all at once by using the characteristic liquid pumping system of the present invention.

The liquid pumping system of the present invention means a storage tank (17) whose liquid contact part is a non-metallic material, a sulfuric acid supply pipe (11) to the storage tank, a sulfuric acid discharge pipe (19) from the storage tank, and a storage tank. The system includes a gas supply pipe (13) to the tank and a gas discharge pipe (15) from the storage tank. Examples of the non-metal material forming the liquid contact portion of the storage tank include a fluororesin such as Teflon and a ceramic material such as high-purity SiC produced by the CVD method. Examples of the gas used in the liquid pressure feeding system include clean gases such as air and nitrogen, but clean air is preferable. The gas pressure is 1.
It is about 0 to 2.0 kg / cm ² G.

The temperature of sulfuric acid at the outlet of the cooler installed upstream of the intermediate tank is preferably 60 to 120 ° C. If the temperature is too low, the effect of stripping the sulfurous acid gas in sulfuric acid may be insufficient, while if the temperature is too high, metal elution may be promoted.

The method of using the liquid pumping system is as follows. The sulfuric acid in the intermediate tank (9) is supplied to the storage tank (17) by gravity through the sulfuric acid supply pipe (11). At this time, the storage tank outlet valve (18) is closed, and the sulfuric acid is stored in the storage tank. Next, the storage tank inlet valve (12) is closed, the storage tank outlet valve (18) is opened, and the gas is supplied from the gas supply pipe (13) to the storage tank to the storage tank, whereby the sulfuric acid in the storage tank is discharged. Is pumped from the storage tank. At this time, the gas outlet valve (16) is closed. When the delivery of the sulfuric acid in the storage tank is completed, the gas inlet valve (14) is closed, the gas outlet valve (16) is opened, and the sulfuric acid in the intermediate tank (9) is supplied to the storage tank (17) again. Enter the cycle. Thus, the sulfuric acid is transported. It should be noted that the liquid pumping system is provided with two or more units arranged in parallel to the flow of sulfuric acid, and is operated by shifting the time cycle for each unit, whereby more continuous circulation of sulfuric acid becomes possible. The above-described operation of the liquid pressure feeding system can be automatically performed by using a normal automatic control system.

In this step, at least a part of the sulfuric acid is supplied to the stripping step, while the remaining part of the sulfuric acid is recycled to the absorption step.

In the stripping step of the present invention, in the stripping tower (10), the sulfuric acid supplied from the transportation step is stripped with air (4) to separate and remove the sulfurous acid gas in the sulfuric acid from the sulfuric acid. This is a step of obtaining higher purity sulfuric acid (3). As a stripping tower,
The same tower as the absorption tower described in the absorption step can be used. In this step, for example, a method in which sulfuric acid to be stripped is supplied from the upper part of the stripping column and air is supplied from the lower part of the stripping column to bring them into contact with each other in the stripping column can be mentioned.

In the present invention, as a modification of the above, the stripping step and the transportation step may be as follows (FIG. 2).

Stripping step: Sulfuric acid (7) supplied from the absorption step in the stripping tower (10)
To obtain higher purity sulfuric acid (3) by stripping the sulfur with air (4) to separate and remove the sulfurous acid gas in the sulfuric acid from the sulfuric acid

Transport step: a step of branching and collecting at least a part of the sulfuric acid supplied from the stripping step as product sulfuric acid, in which the sulfuric acid supplied from the absorption tower is cooled by a cooler (8) and then an intermediate tank ( Stored in 9),
Further, the sulfuric acid in the intermediate tank is stored in a storage tank (17) whose liquid contact part is made of a non-metallic material, a sulfuric acid supply pipe (11) to the storage tank, a sulfuric acid discharge pipe (19) from the storage tank, and a gas to the storage tank. A step of transporting sulfuric acid by a liquid pumping system including a supply pipe (13) and a gas discharge pipe (15) from a storage tank.

For the details of the above method, the method described above can be applied correspondingly.

The high-purity sulfuric acid obtained by the production method of the present invention can have a metal content concentration of 10 weight ppt or less and a sulfurous acid gas concentration of 1 weight ppm or less, and is optimally used as a cleaning liquid for a silicon wafer used in a semiconductor factory. Can be done.

[0020]

Next, the present invention will be described by way of examples.

EXAMPLE 1 89% by weight of sulfuric acid 20 in a Teflon tank (200 l)
0 kg was charged, and liquid circulation was performed for 24 hours at a liquid temperature of 80 ° C. and an average flow rate of 8 l / hr by the liquid pressure feeding system of the present invention. The liquid pumping system used here is a storage tank (capacity 20 l) whose liquid contact part is made of Teflon which is a non-metallic material,
Sulfuric acid supply pipe to the storage tank, sulfuric acid discharge pipe from the storage tank,
It is a system (FIG. 3) including a gas supply pipe to the storage tank and a gas discharge pipe from the storage tank. Clean air having a pressure of 2.0 kg / cm ² G was used as the gas in the liquid pressure feeding system. The results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that a Teflon centrifugal pump was used instead of the liquid pumping system and the average flow rate was 8 l / hr. The results are shown in Table 1.

[0023]

[Table 1] ------------------ Circulation Before Circulation After Circulation Example 1 Comparative Example 1 Circulation After sulfuric acid Metal content of ppt Aluminum 10 12 1100 Copper 2 3 1200 Magnesium 5 5 112 Iron 14 15 2175 −−−−−−−−−−−−−−−−−−−−−−−−−−−−−− −

[0024]

As described above, according to the present invention, it is possible to provide a method for producing highly pure sulfuric acid from which impurities such as metal components and sulfurous acid gas are highly removed.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a flow of the present invention.

FIG. 2 is a diagram showing an example of a flow of the present invention.

FIG. 3 is a diagram showing a flow of the first embodiment.

[Explanation of symbols]

 1 Sulfuric acid 2 Water 3 High purity sulfuric acid 4 Air 5 Vent 6 Absorption tower 7 Sulfuric acid 8 Cooler 9 Intermediate tank 10 Stripping tower 11 Sulfuric acid supply pipe 12 Storage tank inlet valve 13 Gas supply pipe 14 Gas inlet valve 15 Gas discharge pipe 16 Gas outlet valve 17 Storage tank 18 Storage tank outlet valve 19 Sulfuric acid discharge pipe

Claims (4)

[Claims] 1. High-purity sulfuric acid (3) from gaseous anhydrous sulfuric acid (1) containing sulfurous acid gas as an impurity and water (2)
A method for producing high-purity sulfuric acid, which comprises the steps of: Absorption step: In the absorption tower (6), water (2) and gaseous sulfuric acid anhydrous (1) are brought into contact with each other to absorb the gaseous anhydrous sulfuric acid into the water so that sulfuric acid containing sulfurous acid gas as an impurity ( 7) Step of obtaining: Transporting step: a step of transporting and supplying at least a part of sulfuric acid to the following stripping step, wherein the sulfuric acid supplied from the absorption tower is cooled by a cooler (8) and then transferred to an intermediate tank (9). The sulfuric acid stored in the intermediate tank is further stored in a storage tank (17) whose liquid contact portion is made of a non-metallic material, a sulfuric acid supply pipe (11) to the storage tank, a sulfuric acid discharge pipe (19) from the storage tank, and a storage tank. For transporting sulfuric acid by a liquid pressure-feeding system including a gas supply pipe (13) to the tank and a gas discharge pipe (15) from the storage tank Stripping process: Sulfur supplied from the transportation process in the stripping tower (10). Step of obtaining the air (4) in the scan trippin ring to high purity sulfuric acid than Nisato to separate and remove sulfur dioxide in sulfuric acid from the sulfuric acid (3) 2. The manufacturing method according to claim 1, wherein the transporting step and the stripping step are the following steps. Stripping process: In the stripping tower (10), sulfuric acid (7) supplied from the absorption process is stripped with air (4) to separate and remove sulfurous acid gas in sulfuric acid from sulfuric acid to obtain a higher purity. Step of obtaining sulfuric acid (3) Transport step: a step of branching and collecting at least a part of the sulfuric acid supplied from the stripping step as product sulfuric acid, and the liquid contact part is a non-metallic storage tank (17), storage tank Sulfuric acid is transported by a liquid pumping system including a sulfuric acid supply pipe (11) to the storage tank, a sulfuric acid discharge pipe (19) from the storage tank, a gas supply pipe (13) to the storage tank, and a gas discharge pipe (15) from the storage tank. The process of performing 3. The manufacturing method according to claim 1, which has two or more liquid pumping systems arranged in parallel to the flow of sulfuric acid. 4. The manufacturing method according to claim 1, wherein the gas in the liquid pumping system is air or nitrogen.